1. Field of the Invention
The invention relates to fluorescent lamps which contain mercury, and is directed more particularly to means by which mercury is released into a lamp during manufacture of the lamp.
2. Description of the Prior Art
In FIGS. 1 and 2 there is shown an illustrative capsule 10 of the type to which the present invention pertains. The capsule 10 comprises a metal ribbon 12 comprising a first portion 14 having a depression 16 formed in a surface 18 thereof for receiving and retaining a body of liquid mercury 30 (FIG. 3). The ribbon 12 further comprises a second portion 20 having a protrusion 22 formed on a surface 24 thereof. The protrusion 22 and depression 16 are of complementary configuration. The ribbon 12 still further includes a bendable portion 26 which interconnects the first and second portions 14, 20. The first and second portions 14, 20 are bendably movable to the position shown in FIGS. 2 and 3, and thence to the positions shown in FIGS. 5 and 6, wherein the protrusion 23 is clamped into sealing engagement with the depression 16, to form an enclosed chamber 32 (FIG. 6) in which the mercury 30 is sealingly captured.
The capsule 10 may then be handled in a fluorescent lamp fabrication environment without special provisions for handling mercury, and insuring safety to the environment and to personnel, inasmuch as the mercury is securely sealed in the capsule. Once in the lamp, however, the capsule 10 must be ruptured to permit the mercury to enter the lamp envelope. Rupturing of the capsule is accomplished by means of application of heat to the capsule by way of radio frequency energy directed to the metal of the capsule, preferably nickel plated stainless steel, and the mercury, to raise the temperature of the metal and the pressure of the mercury. The heating of the metal and the pressurization of the mercury serve to rupture the capsule, permitting the mercury to escape into the lamp envelope. Unfortunately, a substantial portion of the lamp is heated during the capsule rupturing step, including portions which can be deleteriously affected by exposure to high heat.
It is deemed beneficial to provide a capsule of similar structure, but with facility for releasing mercury at lower temperatures which do not risk damage to other portions of the lamp.
An object of the invention is, then, to provide a mercury capsule for use in fluorescent lamps, which capsule retains the advantages of the above described capsule, and which, in addition, is capable of releasing the mercury into the lamp when acted upon by a relatively low temperature.
A still further object of the invention is to provide such a capsule capable of releasing its full content of mercury in a relatively short time.
With the above and other objects in view, as will hereinafter appear, a feature of the present invention is the provision of a mercury capsule for use in a fluorescent lamp, the capsule comprising a shell defining a chamber and a bore extending through the shell, a body of mercury disposed in the chamber, and a plug sealing the bore, the plug having a melting point less than a melting point of the capsule otherwise, to melt from the bore to open an exit passageway for the mercury.
In accordance with a further feature of the invention, there is provided a fluorescent lamp having an envelope of light-transmitting vitrous material, having opposed end portions and containing an inert gas. First and second electrodes are respectively disposed within the opposed end portions, and a pair of lead-in wires are connected to each of the electrodes. A mercury capsule is secured to one of the lead-in wires. The mercury capsule comprises a shell defining a chamber and a bore extending through the shell, a body of mercury disposed in the chamber, and a plug sealing the bore, the plug having a melting point less than a melting point of the capsule otherwise, to melt from the bore to open an exit passageway for the mercury.
In accordance with a still further feature of the invention, there is provided a method for making a mercury capsule for use in a fluorescent lamp. The method comprises the steps of forming a metal shell for receiving a body of mercury, forming a bore in the shell, closing the bore with molten metal, and permitting the molten metal to solidify to form a plug in the bore. The method includes the further steps of depositing a body of mercury in the shell, and sealing the shell closed with the body of mercury therein. The plug exhibits a melting point reached in manufacture of the lamp, to melt from the bore to open an exit passageway for the mercury.
The above and other features of the invention, including various novel details of construction and combinations of parts and method steps, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular devices and methods embodying the invention are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.